This invention relates to a method and apparatus for treating paper with material in repetitive patterns. More particularly, the invention relates to a method and apparatus whereby these repetitive treatment patterns can be applied without contact between the paper and the apparatus.
It is well known in the papermaking art that it is desirable to have the capability to alter or enhance the characteristics of paper. For instance, cigarette manufacturers have long appreciated the usefulness of adding flavorings or burn control additives to paper. Another more recent application that has been identified concerns altering cigarette paper so that smoking articles incorporating the altered paper will have a reduced burn rate when the smoking article is not drawn on by the smoker; but have the same feel, taste and burn when drawn on by the smoker at normal intervals.
Cigarette wrappers, i.e., papers, have burn characteristics, including burn rates and static burn capabilities. It is known that burn characteristics can be modified by adding fillers, coatings, or additives to papers. Copending, commonly-assigned U.S. patent application Ser. No. 07/614,620 includes a description of many of these methods, and also discloses a nonlaminated paper of variable basis weight and suggests that burn rate control of this paper can be achieved economically with mass-production techniques. The variable basis weight is achieved by applying bands of slurry in a pattern to a moving paper web during production while leaving regions of the paper between the pattern untreated. Additional slurry increases the basis weight of the paper in treated regions, and when the paper is incorporated in a smoking article, the smoking article has a decreased burn rate in these regions. Although many methods are known for treating paper with material in patterns, limitations of these methods render them less effective for altering the basis weight of cigarette paper in patterns.
For example, many techniques have been developed for imprinting or coating paper webs. These include gravure presses, blade coating, roller coating, silkscreening and stenciling methods. Bogardy U.S. Pat. No. 4,968,534 describes a stenciling apparatus wherein a continuous stencil comes into facing engagement with a paper web during the application procedure. The apparatus includes a preparation step where air is evacuated from the web through the pattern stencil prior to the application step in order to facilitate the treatment procedure. The pattern applied by the device can be altered by changing the stencil used.
The apparatus of Bogardy U.S. Pat. No. 4,968,534 is typical of many of the other previously known treatment devices because the apparatus contacts the paper web during the application process. These previously known devices, as a result, can only be used at points in the papermaking process where the paper is sufficiently stable to withstand the contact. This limits flexibility in placement of these devices, because the devices cannot be incorporated in a papermaking machine at relatively early stages of the papermaking process.
Stenciling and other previously known methods generally transfer a predetermined pattern to a treated article. The only way to change the pattern applied is to replace the pattern-forming element of the device. In other words, there is no easy way to alter the pattern by, for instance, merely changing operating parameters. This characteristic particularly limits the applicability of these devices in mass-production situations where it is desirable to apply several patterns to paper being produced.
Another characteristic of previously known devices like that of Bogardy U.S. Pat. No. 4,968,534 is that the amount of material applied cannot be varied appreciably. In essence, since the devices are in contact with the web, there must be penetration of the web by the material during the application procedure for significant amounts of material to be applied to the web. The required penetration may not be possible depending on the combined characteristics of the paper and the treatment material, thereby resulting in less than optimum treatment of the paper.
A particular limitation of devices like that of Bogardy U.S. Pat. No. 4,968,534 is that a stenciling device incorporating a pattern for applying relatively-closely spaced bands of narrow width to cigarette paper would experience flexure of the stencil and resultant pattern non-uniformity when scaled to the size of a papermaking machine of the type used to make cigarette paper.
A final characteristic of previously known devices is that in order to maintain sufficient pressure, a sump of treatment material is positioned above the stencil. This solution generally requires that sump material be recirculated to a reservoir. This constant recirculation of unused treatment material may allow contamination of the treatment material.
It would be desirable to provide a method and apparatus for treating paper webs which can be easily incorporated into present papermaking machines.
It would be desirable to provide a method and apparatus for treating paper webs without contact between the paper web and the apparatus.
It would be desirable to provide a method and apparatus for applying chemical treatments to paper webs in patterns wherein the pattern applied can be altered by changing machine operating parameters.
It would be desirable to provide a method and apparatus for treating paper webs where the pattern applied can also be altered by replacing the pattern forming element of the apparatus.
It would be desirable to provide a method and apparatus for applying material to moving paper webs where the amount of material applied can be varied appreciably.
It would be desirable to provide a method and apparatus for applying material to moving paper webs in uniform patterns.
It would be desirable to provide a method and apparatus for applying material to moving paper webs where the amount of material being applied can be accurately metered, eliminating the need for recirculation of treatment material.
It would further be desirable to provide a method and apparatus for applying chemical treatments to cigarette paper so that burn rate control can be achieved economically with mass production techniques.